Sonographic findings in three cases of carcinoma showing thymus-like differentiation

Carcinoma showing thymus-like differentiation (CASTLE) is a rare tumor of the thyroid gland or soft tissues of the head and neck. To our knowledge, there have been only a few reports concerning imaging findings of CASTLE. We report herein the sonographic appearances of three cases of CASTLE. Two tumors were located at the lower part of the thyroid and one had spread throughout the thyroid. Sonograms showed heterogeneously solid tumors without cystic components or calcification. The central part of the tumor was slightly hyperechoic compared with the peripheral part of the tumor. Histologically, the tumors were composed of a mixture of fibrous stroma and epithelial nests.